Light leakage detection in edge sealants of optical devices

ABSTRACT

Techniques are described for inspecting optical devices, such as eyepieces, to determine whether they exhibit light leakage through an edge sealant that has been applied to the device. Embodiments provide an inspection apparatus that can be employed to detect the leakage of light through an edge sealant of an optical device, where the edge sealant is applied to prevent, or at least reduce, the leakage of light from the optical device. Light from a light source is projected into the optical device. The light can travel along one or more wave guides within the device, until reaching an edge of the device. Light that is able to leak through an edge sealant can be reflected, using mirror(s) in the apparatus, and detected by a camera. Image(s) captured by the camera can be analyzed to determine the performance of the optical device with respect to edge leakage.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.16/438,683 entitled “LIGHT LEAKAGE DETECTION IN EDGE SEALANTS OF OPTICALDEVICES” and filed on Jun. 12, 2019, which claims the benefit of U.S.Application No. 62/684,478 entitled “LIGHT LEAKAGE DETECTION IN EDGESEALANTS OF OPTICAL DEVICES” and filed on Jun. 13, 2018, both of whichare incorporated by reference herein in their entirety.

BACKGROUND

In optical devices, light can be directed and/or manipulated to achievea desired effect. For example, in an optical device such as an eyepieceused in a virtual reality interface, visible light can be directedand/or manipulated to provide image data that is perceived by a user.Various types of optical devices may be subjected to testing, duringand/or after manufacture, to ensure that the devices are manufacturedand/or operate according to desired specifications. For example, in sometypes of optical devices, it may be advantageous to reduce or eliminatethe leakage of light out of the device.

SUMMARY

Embodiments of the present disclosure are generally directed totechniques for detecting light leakage from optical devices. Morespecifically, embodiments are directed to at least one apparatus and/orat least one method for detecting and quantifying light leakage througha sealant that is applied to edge(s) of an optical device such as aneyepiece.

In general, innovative aspects of the subject matter described in thisspecification can be embodied as an inspection apparatus that includes:a stage including a surface, an opening, and one or more mirror supportstructures that each supports a respective mirror; a light source thatis below the stage and that is arranged to project light through theopening of the stage and into a portion of the eyepiece when theeyepiece is resting on the surface of the stage, the eyepiece havingmultiple optics layers and an edge sealant along at least one edge ofthe eyepiece; an enclosure that encloses the stage and the light sourceto isolate the eyepiece from external light from outside the enclosure;and a camera that is arranged to capture, through an aperture in theenclosure, at least one image of an interior of the enclosure, the atleast one image including at least a portion of the light that leaksthrough the edge sealant of the eyepiece and that is reflected to thecamera by the at least one mirror.

Embodiments can optionally include one or more of the followingfeatures.

In some embodiments, the inspection apparatus further includes ananalysis module that receives the at least one image from the camera andthat analyzes the at least one image to quantify light leakage throughthe edge sealant of the eyepiece.

In some embodiments, the stage further includes a block that is betweenthe opening and the camera and that prevents the light projected by thelight source from directly reaching the camera.

In some embodiments, the one or more mirror support structures eachsupports the respective mirror to be disposed at approximately a 45degree angle with respect to the surface of the stage.

In some embodiments, the camera includes a telecentric lens.

In some embodiments, the apparatus includes the eyepiece.

In some embodiments, the projected light is white light.

In some embodiments, the light is projected into the portion of theeyepiece that includes at least one color filter to separate the whitelight into a plurality of color bands.

In some embodiments, the eyepiece includes multiple layers, each layerof the multiple layers including a respective wave guide for aparticular color band.

In some embodiments, the at least one image includes pixels of at leastone color band to indicate light leakage through the edge sealantcorresponding to at least one particular layer of the eyepiece.

In general, innovative aspects of the subject matter described in thisspecification can be embodied as a method of inspecting an eyepiece,including positioning an eyepiece on a stage defining an opening,wherein the eyepiece comprises an edge sealant along at least one edgeof the eyepiece; enclosing the stage to isolate the eyepiece fromexternal light outside the enclosure; providing light from a lightsource inside the enclosure through the opening and toward the eyepiece;capturing, through an aperture in the enclosure, an image of an interiorof the enclosure; and assessing, based on the image, light leakage fromthe eyepiece through the edge sealant.

Embodiments can optionally include one or more of the followingfeatures.

In some embodiments, light from the light source comprises white light.

In some embodiments, the eyepiece comprises a color filter configured toseparate the white light into a plurality of color bands, and the methodfurther includes providing the light toward the eyepiece comprisesproviding the light to the color filter. The eyepiece can includemultiple optics layers, each layer of which includes a wave guide for aparticular color band, and the image includes pixels of at least onecolor band, thereby indicating leakage of the light through the edgesealant corresponding to at least one layer of the multiple opticslayers.

Some embodiments include identifying a number of layers of the multipleoptics layers through which leakage of the light occurs.

Some embodiments include identifying a location on the eyepiececorresponding to the leakage of the light. Some embodiments includeidentifying, based on the pixels of the at least one color band, the atleast one layer associated with the leakage of the light. Someembodiments further include assessing a number of the pixels of the atleast one color band in the image.

It is appreciated that aspects and features in accordance with thepresent disclosure can include any combination of the aspects andfeatures described herein. That is, aspects and features in accordancewith the present disclosure are not limited to the combinations ofaspects and features specifically described herein, but also include anycombination of the aspects and features provided.

The details of one or more embodiments of the present disclosure are setforth in the accompanying drawings and the description below. Otherfeatures and advantages of the present disclosure will be apparent fromthe description and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 depicts a schematic of an example inspection apparatus, accordingto embodiments of the present disclosure.

FIG. 2 depicts a schematic of an example stage included in theinspection apparatus, according to embodiments of the presentdisclosure.

FIG. 3A depicts a schematic of an example optical device that can beinspected using the inspection apparatus, according to embodiments ofthe present disclosure. FIG. 3B depicts a cross-section schematic of anexample optical device that can be inspected using the inspectionapparatus, according to embodiments of the present disclosure.

FIG. 4 is a flow chart showing operations in a process for detectinglight leakage from an optical device.

DETAILED DESCRIPTION

Embodiments of the present disclosure are directed to techniques fordetecting light leakage from optical devices. In particular, embodimentsprovide an inspection apparatus that can be employed to detect theleakage of light through an edge sealant of an optical device, where theedge sealant is applied to prevent, or at least reduce, the leakage oflight from the optical device. In some examples, the optical devicebeing inspected is an eyepiece that has been manufactured for use in avirtual reality, augmented reality, and/or computer vision interfacedevice, or to deliver images data, video data, graphics data, and/orother types of visually perceivable information to a user who is wearingor otherwise using the interface device.

In some examples, manufacture of an eyepiece can include the applicationof a polymer sealant, or other type of sealant, around the edge(s) ofthe eyepiece. The sealant may accordingly be described as an edgesealant. The sealant may be applied to absorb light coming out of theeyepiece, and to prevent light from reflecting back into the eyepieceand degrading optical performance of the eyepiece. In experimentsconducted on an example eyepiece, when sealant is applied in a faultymanner with gaps, flaws, or inconsistencies, tests showed that theeyepiece exhibited optical defects such as degraded contrast. To ensurethe quality and performance of the eyepiece, the inspection apparatusdescribed herein can be used to detect flaws in the sealant coverage,such as gaps, inconsistencies, or irregularities that could allow lightreflection that may degrade the performance of the eyepiece. In additionto providing structural support for the multi-layer eyepiece, the edgesealant also acts as a light sink, preventing light from being reflectedback into the waveguides of the eyepiece as the light reaches the edgeof the eyepiece. The light leakage, which can be detected using thetechniques described herein, may not directly affect eyepiece quality,but it provides an indicator of poor edge seal coverage which may leadto light reflection which affects the contrast of the eyepiece.

FIG. 1 depicts a schematic of an example inspection apparatus 100,according to embodiments of the present disclosure. The inspectionapparatus 100 is also described herein as the apparatus. The apparatus100 can include an enclosure 102 that is composed of a material and/orconstructed to prevent external light from entering the interior of theenclosure 102. In some embodiments, the enclosure 102 is black. Theenclosure 102 can include four walls, a bottom, and a top, as shown inthe example of FIG. 1. In some embodiments, a front wall of theenclosure 102 is a (e.g., sliding and/or removable) wall that functionsas a door to provide access to the inside of the enclosure 102. Thiswall may be closed during operation of the inspection apparatus. FIG. 1shows an example in which this wall is open, to show the stage 104 andlight source 106 inside the enclosure.

The stage 104 can be configured to support an eyepiece or other type ofoptical device that is being inspected. The stage 104 is describedfurther with reference to FIG. 2. The light source 106 can be arrangedbelow the stage 104, and disposed to project light upward into a portionof the eyepiece that has been placed on the stage 104. The stage 104 canbe supported by one or more (e.g., four) stage supports 112, which holdthe stage 104 at an appropriate distance above the bottom of theenclosure 102, to provide sufficient clearance for the light source 106under the stage 104. In some embodiments, the light source 106 is atleast one light emitting diode (LED). In some embodiments, the lightsource 106 emits white light. By enclosing the light source 106 andstage 104 (and eyepiece being tested) within the substantially darkinterior of the enclosure 102, the apparatus 110 can ensure that littleor no external light is able to penetrate to the eyepiece while it isbeing inspected for edge sealant light leakage.

The apparatus 100 can also include at least one camera 110. In someembodiments, a single camera 110 is employed, and the camera 110 mayinclude a telecentric lens. The camera 110 may be disposed above thestage 104 and eyepiece, and may have visibility to the interior of theenclosure 102 through an aperture in the top of the enclosure 102.Through the aperture, the camera 110 can capture one or more images ofthe interior of the enclosure while the light source 106 is illuminatinga portion of the eyepiece resting on the stage 104. The capturedimage(s) can be of a field of view that includes the stage 104, theeyepiece on the stage 104, and any light reflected by the mirror(s) onthe stage 104. The image(s) can be analyzed to determine whether theyexhibit light leakage through the edge sealant of the eyepiece beinginspected, as described further below.

In some embodiments, the camera 110 is communicatively coupled to ananalysis component, such as a computing device. In some embodiments, thecamera 110 includes the analysis component (e.g., analysis component111), such that the camera 110 can perform at least a portion of theimage analysis. The image(s) may be communicated to the analysiscomponent via one or more signals that are transmitted, over a wired orwireless connection, from the camera 110 to the analysis component. Theanalysis component can analyze the image(s) to determine whether theeyepiece under inspection is exhibiting any light leakage. The apparatus100 can also include a back plate 114 coupled to the top of theenclosure 102, and a camera holder 116 (e.g., bracket) coupled to theback plate 114, the back plate 114 and camera holder 116 arranged tosecure and stabilize the camera 110 during inspection of an eyepiece.

FIG. 2 depicts a schematic of an example stage 104 included in theinspection apparatus 100, according to embodiments of the presentdisclosure. As shown in the example of FIG. 2, the stage 104 can includea surface 202. The surface 202 can be (e.g., substantially) flat, andshaped to hold the eyepiece(s) to be inspected. An opening 204 throughthe stage 104 and the surface 202 can allow the (e.g., white) lightprojected from the light source 106, below the stage 104, to enter atleast a portion of the eyepiece that has been placed on the surface 202.

In some embodiments, the stage 104 can include a block structure 206that is above the opening 204, such that the eyepiece is between theopening 204 and the block 206, and such that the block 206 is betweenthe eyepiece and the camera 110. The block 206 is arranged to preventlight projected from the light source 106 from directly reaching thecamera 110, which is placed substantially above the opening 204. Theblock 206 can ensure that the camera 110 detects the light that isreflected from the mirrors on the stage 104, but does not detect thelight projected directly from the light source 106.

The stage can include one or more mirror supports 208 that each supportsa mirror. Each mirror can be disposed to reflect any light, travellingoutward in a transverse direction from the edge of the eyepiece, upwardto the camera 110. Accordingly, the mirrors can be arranged at (e.g.,approximately) a 45 degree angle relative to the surface 202. Thus,light that leaks through the edge sealant of the eyepiece, travelling ina substantially horizontal direction outward from the eyepiece, can bereflected upward to travel in a substantially vertical direction towardthe camera 110, and the image(s) captured by the camera 110 can includethe reflected light.

The stage can also be configured to further reduce the effect of straylight. The eyepiece can sit on the raised support in noncritical areasand the lip of the stage can be slightly higher than the bottom ofeyepiece to block stray light between eyepiece and stage which canotherwise be difficult to filter out.

The (e.g., slit) mirror(s) can image the vertical edge of eyepiece intohorizontal virtual images to be captured by the telecentric lens.Leakage within the numerical aperture (NA) of the mirror(s) and the NAof the lens can be collected on the camera. In some instances, theleakage may be well-focused (e.g., for orthogonal pupil expander (OPE)leakage) such that the structure of all (e.g., six) layers of waveguidesare clearly visible. In other instances (e.g., incoupling grating (ICG)leakage), the leakage can be less focused.

The inspection apparatus illuminates the eyepiece with light from thelight source 106. The light then travels through the wave guides of theeyepiece per the design of the eyepiece, until it reaches the edgesealant. Ideally, the edge sealant would prevent the light from leakingthrough the edge sealant, or reflecting back into the eyepiece, thusdegrading the optical performance of the eyepiece. Any light that leaksthrough the edge sealant can be reflected upward by the mirror(s) andcaptured by the camera 110. Thus, the image(s) captured by the camera110 can be analyzed to determine whether the eyepiece being examinedexhibited light leakage through the edge sealant, indicating a flaw inthe edge sealant.

In some embodiments, the white light from the light source 106 can beprojected into a portion of the eyepiece that includes one or morefilters, which split the white light into different color bands (e.g.,ranges of wavelengths), such as different bands for red, green, andblue. The eyepiece can be designed with multiple layers, each layerproviding a wave guide that is configured to guide a particular colorband of the light. Thus, the filter(s) of the eyepiece can split thewhite light into different color bands that travel along differentlayers of the eyepiece. Any light escaping through the edge sealant canbe in one or more of the color bands. Accordingly, the apparatus 100 canemploy a color camera 110 that distinguishes the different colors oflight. The different colors of light detected by the camera 110 canindicate light leakage through the edge sealant at the level, in theeyepiece, of the layer(s) that convey the detected colors of light.Thus, by distinguishing the color of the leaked light, the apparatus 100can provide information regarding which layer(s) of the eyepiece thelight is leaking from. The color camera is used to distinguish actualleakage (e.g., red, blue, or green) from stray light (e.g., white) thatmainly includes from the LED light source, and some small amount ofambient light leaking into the enclosure. The LED can be high power, andthus exposure time is minimal, reducing the impact of surroundingenvironment. By distinguishing colors, the system can determine whichlayer the leakage is from, at least with respect to distinguishingleakage from layers that are waveguides for light of a different color(e.g., distinguishing red from green layers).

In some embodiments, analysis of the image(s) can include counting anumber of pixels, in the image(s), for each detected color band (e.g.,red, green, or blue). The pixel count(s) can be used to develop aquality metric for the eyepiece, indicating the leakage that is detectedand that corresponds to the various layers in the eyepiece. Becausedifferent layers of the eyepiece have waveguides for differentwavelength bands (color bands) of light, the differences in colorleakage can indicate sealant problems at different layers in theeyepiece, such as insufficient sealant coverage at particular layer(s)that are the particular waveguide(s) for particular frequency band(s).If there is faulty sealant coverage at multiple layers, the image(s)could exhibit different colors of leaked light.

In some embodiments, the image(s) may be further examined to detect thelocation, in the image(s), of the light bands corresponding toedge-leaked light. The determination of the faulty layer(s) can be basedon the detected locations of the light bands in the image(s). Forexample, six active layers leaking light from the edge could cause up tosix bands of detected light leakage in the image(s). Color filtering inthe captured image(s) and/or in the camera 110 itself could also reducethe effect of any stray light that penetrates to the interior of theenclosure 102, by filtering out the stray (e.g., white) light that maypenetrate into the apparatus 100 from the exterior.

Based on the location of the light leakage from the edge, and becausethe mirror(s) are angled, light traveling out of the edge of a top layertravels further before reaching the mirror than light coming out of theedge of a bottom layer. Light from a top layer is seen by the camera asbeing further away from the center of an eyepiece than light coming froma bottom layer. This can help distinguish light leak areas if there aremultiple layers guiding the same wavelength of light. For example, ifthere are two green layers within the eyepiece, this angled mirrorsystem can distinguish which green layer a leak originates from based onthe location of the light band in the image.

In some embodiments, the mirror(s) are disposed at a 45 degree anglerelative to the broad surface of the eyepiece, or at approximately a 45degree angle within a tolerable angular error. Other arrangements of themirror(s) and camera can also be supported by embodiments. The 45 degreeangled configuration enables the mirror(s) to reflect a vertical edgeinto a horizontal image for the telecentric lens, such that the edgesthat that are equally away from mirrors are equally well focused. Theremay be some difference in the case of the ICG area where the edge iscurved toward the mirror, and the telecentric lens that is used can havea sufficient focal depth to accommodate this.

In some embodiments, the eyepiece can be illuminated with differentwavelengths of light (different colors) to probe for any possibleleakage at the different layers of the eyepiece. Alternatively, theeyepiece can be illuminated with white light, and the filter(s) in theeyepiece can split the light into constituent colors for the differentlayers to convey. This latter example may test the eyepiece undersimilar conditions to its normal operating conditions (e.g., in avirtual reality interface).

The use of multiple mirrors along the various edges of the eyepiece canallow one image to be captured that includes any light that may beleaking from any or all of the edges of the eyepiece. This may simplifythe apparatus by enabling use of a single camera and providing a singleset of images to be analyzed, instead of using multiple cameras thatvisualize the various edges and/or using a camera that moves around theedges of the eyepiece. Use of the mirrors inverts the light, and thisinversion may be accounted for in the analysis of the image(s).

In some instances, different regions of the edge of the eyepiece may bemore or less important with respect to performance of the eyepiece, andedge leakage in different regions may have a greater, or smaller, impacton the overall optical performance of the eyepiece. Thus, use of theinspection apparatus 100 can attempt to identify light leakage that mayhave a larger than tolerable impact on the overall performance of theeyepiece, based on which regions of the edge exhibit the detected lightleakage. In general, the image(s) may be captured of an entire region ofinterest (ROI) that includes the entire edge of the eyepiece, and thesubsequent image analysis can determine the overall quality of theeyepiece based on any detected light leakage and based on the relativeimportance of the various edge regions that exhibit the light leakage.

FIG. 3A depicts an example optical device 300 that can be inspectedusing the inspection apparatus 100, according to embodiments of thepresent disclosure. Optical device 300 can be an eyepiece. FIG. 3Bdepicts a cross-section of optical device 300. The view shown is of across-section of an example eyepiece. As shown, the eyepiece can includemultiple layers 302 that each provides a waveguide for a particularwavelength band of light. For example, different layers may be designedto guide red, green, or blue light. An edge sealant 304 may be appliedto the edge of the eyepiece as shown, to attempt to prevent lightleakage 310 from the interior to the exterior of the eyepiece in atransverse direction through the edge. The edge sealant 304 may alsoprevent reflection of light back into the interior of the eyepiece. Theedge sealant 304 may be applied with an appropriate thickness 306, andmay penetrate into the eyepiece, between the layers 302, to anappropriate depth 308. The eyepiece may be composed of multiple layersof (e.g., high index) glass in a stack.

The inspection apparatus described herein can be applied to any suitabletype of optical device. In some examples, the eyepiece may be created atleast in part using Jet and Flash Imprint Technology (J-FIL™), developedby Molecular Imprints™. The J-FIL technique may be used to creatediffraction gratings on the layers of the glass of the eyepiece tocreate waveguide displays. Each layer may be a thin layer of glass withpolymer gratings created on its surface using J-FIL. The diffractiongratings may provide the basic working functionality of the eyepiece.Once the diffraction gratings are formed onto a large, broad glasslayer, the glass layer may be laser cut into the shape of the eyepiece.Other suitable substrate materials can also be used. Each layer of glassmay be a different color, and there may be multiple depth planes. Alarger number of planes may provide for a better virtual experience fora user using the eyepiece. The layers may be stacked using the sealantpolymer (e.g., glue dots), and the whole stack may be sealed using thesealant. Air gaps between the layers may be preserved for the opticalperformance of the eyepiece. The gaps between the layers may havecontrolled dimensions (e.g., substantially uniform width). The edgesealant polymer may be applied around the edge of the layered structureto seal the stack and air gaps from the outside environment. The edgeseal glue also provides a physical lock to ensure mechanical integrityof the structure, while keeping out contamination and moisture. Withoutsuch a seal, the layers may fall apart and delaminate from one another.The gap between layers may be of any suitable width to achieve thedesired optical functionality. The leakage detection system describedherein can be used to detect light leakage in eyepieces of anyappropriate waveguide material.

The use of the sealant enables creation of high contrast eyepieces byabsorbing stray light that hits the edges of the eyepiece layers. Thesealant also provides structural integrity for (e.g., “locks in”) themechanical gap and co-planarity of the eyepieces. The eyepiece may haveany suitable number of layers 302 of glass or other material, and eachlayer may act as a waveguide to allow the passage of various frequenciesof light. Layers may be configured for particular wavelengths, so as topropagate light of a particular color, and the eyepiece may beconfigured for a particular optical power, to create a number of depthplanes at which light through the waveguide may be perceived. Forexample, a first set of waveguide layers may include layers for red,green, and blue at a first depth plane, and a second set of waveguidelayers may include a second set of layers for red, green, and blue lightcorresponding to a second depth plane. The order of the colors may bearranged differently in different depth planes to achieve the desiredoptical effects in the eyepiece. In some embodiments, a single (e.g.,blue) layer may cover multiple depth planes. In some examples, the edgesealant may be a glue, resin, polymer sealant, ink, and/or other viscousmaterial. The edge sealant may be black. Blackening an edge of themulti-layer eyepiece may cause the absorption of light impinging on theedge, and/or provide for reduced reflection of light impinging on theedge.

An image generated by the inspection apparatus 100 may be captured bythe camera 110 during the inspection of the eyepiece for edge leakage.Any detected leakage may manifest itself in the image as one or morebands of (e.g., different colored) light, indicating that one or morelayers of the eyepiece are exhibiting leakage.

In some embodiments, the eyepiece is illuminated through the colorfilter(s) of the eyepiece with a light source 106 that is a white spotLED. The red-green-blue (RGB) light filtered through the color filter(s)travel through the eyepiece, through a particular light path (e.g., ICGto OPE to exit pupil expander (EPE) to eye) in all of the layers of theeyepiece, in the same way as it would travel when the eyepiece is beingused in the end product (e.g., a virtual reality interface projector andwearable). If an edge of a glass layer is not sufficiently covered byedge sealant polymer, light can leak out from the waveguide, bereflected by the mirror(s), and be imaged by the (e.g., telecentric)lens and color camera. By extracting colored pixels in the leakage ROIwith a color library trained by testing actual eyepieces, the area ofpoor or no coverage can be calculated for each color at each ROI. Asdescribed above, different edge regions may provide different ROIs,which have different impacts on eyepiece optical performance. Weightedmetrics can be derived from leakage in each of the ROIs to evaluatetotal impact due to edge leakage.

In some examples, the regions are listed in order of importance toeyepiece performance, the EPE bottom (more important), the ICG, and theOPE (less important). Due to how light travels inside the eyepiece,different ROIs can exhibit different amounts of leakage even when edgeseals in the different regions are comparable in quality. For example,the ICG and OPE interior (e.g., nasal) sides may be easiest to inspect,due to abundant leakage. The OPE top side did not exhibit substantialleakage during testing, perhaps because the OPE grating does not lose alarge amount of light in that direction. The EPE bottom did not exhibitmuch leakage in an eyepiece with severe leakage in the ICG and OPEareas, perhaps because significant light loss had already occurredthrough ICG and OPE prior to reaching EPE bottom. In some examples, foreyepieces with severe EPE-only leakage, green leakage was detectable,and red and blue leakage were not as prominent. Eyepieces may beinspected in the apparatus multiple times to ensure sufficient datacollected for analysis and to diagnose possible issues present in theeyepieces. In some examples, total pixel counts of RGB in all ROI may beused as an overall metric for eyepiece quality. Different metricsweighted according to the differing ROI significance can also bederived. In some instances, a threshold metric can be applied todetermine whether the eyepiece passes or fails inspection.

The inspection apparatus 100 can employ any suitable type of camera 110,such as a camera manufactured by Cognex™. In some embodiments, the stage104 may be configured to support left and right eyepieces forinspection, where the left and right eyepieces have substantially thesame shape and inverted. The left and right eyepieces can be laterassembled into the wearable for commercial use. A vacuum pen or othersuitable mechanism can be used to place an eyepiece on the stage 104 andremove the eyepiece from the stage 104. The apparatus 110 may be of anyappropriate size. For example, the apparatus 100 (e.g., the enclosure)may have dimensions of 45 cm by 45 cm by 70 cm (height).

Referring to FIG. 4, process 400 for inspecting an eyepiece includesseveral operations. In 402, an eyepiece having an edge sealant along atleast one edge of the eyepiece is positioned on a stage defining anopening. The eyepiece typically includes multiple optics layers, eachlayer of which includes a wave guide for a particular color band. Insome cases, the eyepiece includes a color filter configured to separatethe white light into a plurality of color bands. In 404, the stage isenclosed to isolate the eyepiece from external light outside theenclosure. In 406, light is provided from a light source inside theenclosure through the opening and toward the eyepiece. The light may beprovided to the color filter configured to separate white light into aplurality of color bands. Light from the light source can be whitelight. In 408, an image of an interior of the enclosure is capturedthrough an aperture in the enclosure. The image may include pixels of atleast one color band, thereby indicating leakage of the light throughthe edge sealant corresponding to at least one layer of the multipleoptics layers. In 410, light leakage from the eyepiece through the edgesealant is assessed based on the image. In some cases, process 400includes identifying a number of layers of the multiple optics layersthrough which leakage of the light occurs. In certain cases, process 400includes identifying a location on the eyepiece corresponding to theleakage of the light. In certain cases, process 400 includesidentifying, based on the pixels of the at least one color band, the atleast one layer associated with the leakage of the light. The number ofpixels of the at least one color band in the image may be assessed.

While this specification contains many specific details, these shouldnot be construed as limitations on the scope of the disclosure or ofwhat may be claimed, but rather as examples of features that areassociated with particular embodiments. Certain features that aredescribed in this specification in the context of separate embodimentsmay also be implemented in combination in a single embodiment.Conversely, various features that are described in the context of asingle embodiment may also be implemented in multiple embodimentsseparately or in any suitable sub-combination. Moreover, althoughfeatures may be described above as acting in certain combinations andeven initially claimed as such, one or more features from a claimedcombination may in some examples be excised from the combination, andthe claimed combination may be directed to a sub-combination orvariation of a sub-combination.

A number of embodiments have been described. Nevertheless, it will beunderstood that various modifications may be made without departing fromthe spirit and scope of the disclosure. For example, various structuresshown above may be used, with elements rearranged, positioneddifferently, oriented differently, added, and/or removed. Accordingly,other embodiments are within the scope of the following claims.

What is claimed is:
 1. An inspection apparatus for inspecting an opticaldevice, the inspection apparatus comprising: a stage including asurface, an opening, and mirror support structures, each mirror supportstructure supporting a respective mirror; a light source arranged toproject light through the opening of the stage and into a portion of theoptical device while the optical device is positioned on the stage; anenclosure that encloses the stage and the light source to isolate theoptical device from external light from outside the enclosure; and acamera arranged to capture, through an aperture in the enclosure, animage of an interior of the enclosure, the image including light thatleaks through a material arranged to reduce leakage of light through anedge of the optical device and that is reflected to the camera by themirror.
 2. The inspection apparatus of claim 1, further comprising: ananalysis module that receives the at least one image from the camera andthat analyzes the at least one image to quantify light leakage throughthe material.
 3. The inspection apparatus of claim 1, wherein the stagefurther includes a block between the opening and the camera thatprevents the light projected by the light source from directly reachingthe camera.
 4. The inspection apparatus of claim 1, wherein the one ormore mirror support structures each supports the respective mirror to bedisposed at approximately a 45 degree angle with respect to the surfaceof the stage.
 5. The inspection apparatus of claim 1, wherein the cameraincludes a telecentric lens.
 6. The inspection apparatus of claim 1,wherein light projected from the light source comprises white light. 7.The inspection apparatus of claim 6, further comprising the opticaldevice.
 8. The inspection apparatus of claim 7, wherein the opticaldevice comprises multiple optics layers, and the material is disposedalong at least one edge of the optical device.
 9. The inspectionapparatus of claim 7, wherein a portion of the optical device comprisesat least one color filter to separate the white light into a pluralityof color bands.
 10. The inspection apparatus of claim 9, wherein eachoptics layer of the multiple optics layers comprises a wave guide for acolor band of the plurality of color bands.
 11. The inspection apparatusof claim 9, wherein the light is projected into the portion of theoptical device that includes at least one color filter.
 12. Theinspection apparatus of claim 9, wherein the at least one image includespixels of at least one of the color bands to indicate light leakagethrough the material corresponding to at least one layer of the multipleoptics layers.
 13. A method of inspecting an optical device, the methodcomprising: positioning an optical device on a stage defining anopening, wherein the optical device comprises a material arranged toreduce leakage of light through an edge of the optical device; the stageto isolate the optical device from external light outside the enclosure;providing light from a light source inside the enclosure through theopening and toward the optical device; capturing, through an aperture inthe enclosure, an image of an interior of the enclosure; and assessing,based on the image, light leakage from the optical device through thematerial.
 14. The method of claim 13, wherein light from the lightsource comprises white light.
 15. The method of claim 14, wherein theoptical device comprises a color filter configured to separate the whitelight into a plurality of color bands, and providing the light towardthe optical device comprises providing the light to the color filter.16. The method of claim 15, wherein the optical device comprisesmultiple optics layers, each layer of which comprises a wave guide for aparticular color band, and the image comprises pixels of at least onecolor band, thereby indicating leakage of the light through the materialcorresponding to at least one layer of the multiple optics layers. 17.The method of claim 16, further comprising identifying a number oflayers of the multiple optics layers through which leakage of the lightoccurs.
 18. The method of claim 16, further comprising identifying alocation on the optical device corresponding to the leakage of thelight.
 19. The method of claim 16, further comprising identifying, basedon the pixels of the at least one color band, the at least one layerassociated with the leakage of the light.
 20. The method of claim 19,further comprising assessing a number of the pixels of the at least onecolor band in the image.